void slvsml_one(double *u, double *rhs)
//Solution of the model problem on the coarsest grid, where h = 1/2 . The right-hand side is input in rhs[1..3] and the solution is returned in u[1..3].
{
  void fill0_one(double *u, int n);
  double h=0.5;
  
  fill0_one(u,3);
  u[2] = -h*h*rhs[2]/2.0;
}
